1. Field of Invention
This invention relates to a linear digital scale and a method of manufacturing the linear digital scale, and in particular to an extended digital scale which utilizes an optical reading system and its manufacturing method.
2. Description of the Prior Art
There has been a well-known measuring instrument which can digitally display the length of measured object or coordinate positions of measured points by the use of a digital scale, the moving part of which is slid corresponding to the measured object. The digital display type measuring instrument finds particular utility in a length measuring machine or a three dimensional coordinate measuring machine. As for the digital display type scale, a digital scale having an optical reading system is of wide use due to the fact that it provides the output signal for digital measuring with high accuracy and reliability. Ordinarily, the optical reading type digital scale has a plurality of slits regularly arranged at equal spaces on the surface of a long and thin glass scale. When the scale is moved corresponding to the length of a measured object, the passing numbers of slits are photo-electrically counted to show the length on a digital display by detecting the counted value.
The afore-mentioned digital scale is suitable for the accurate measurement with inconsiderable reading error but it is difficult to arrange the slits on the scale surface with high accuracy. In particular it is extremely difficult to obtain a long scale.